The present invention relates in general to an apparatus for powering x-ray tubes. More particularly, the invention relates to an improved high voltage single-phase power supply for providing x-ray exposures ranging from repetitive short duration x-ray exposures to continuous x-ray exposures.
At the present time it is common to employ a three-phase power supply to generate power for continuous x-ray generating tubes. These three-phase power supplies are generally complex in construction and costly. Generally speaking, in the past single-phase power supplies have not been employed because the voltage ripple from the rectified signal is too large causing the x-ray tube to produce a lower value x-ray energy than pure D.C. Filtering capacitors are generally impractical at the high voltages that are employed and interfere with switch on-switch off times. Thus, this has resulted in the use of only three-phase systems because these systems have less ripple; ripple being defined as the variation in the D.C. voltage as each phase in sequence contributes to the output voltage level.
The three-phase power supply is generally ineffective in operation when short duration x-ray exposures are desired. With the three-phase system, the x-ray tube is triggered when at least one power supply voltage phase is at a high level resulting in the generation of unwanted and interfering noise. A further limitation occurs when the x-ray image, which results when the x-ray passes through a body, is recorded onto a television-type camera tube. It should be noted here that some other device, such as a fluorescence material or image converter tube, is used between the x-rays and the TV camera to increase the sensitivity of the camera tube. TV circuits have well established sweep rates to which the x-ray exposure must be synchronized. If the exposure is not synchronized, the resulting picture from the TV-type camera has an interference pattern or jitters, which will make the picture very difficult or impossible to view. The exposure thus should be synchronized with the 60 Hz sweep rate to have a coherent picture. It is permissible to have the x-ray exposure be a less frequent multiple of the 60 Hz rate, for example, 30, 15, or 7.5 Hz. In each case, a coherent picture results. The three-phase systems presently being used can only be synchronized by other devices which are complex and costly, such as high voltage tetrodes or grid controlled x-ray tubes.
Also, when the three-phase system is used with short duration x-ray exposures, there are one or more of the phases which are not contributing energy to the x-ray tube. During these phases the high voltage transformer is susceptible to saturation of the transformer core which is highly undesirable.
Accordingly, it is an object of the present invention to provide an improved high voltage power supply which operates from a single-phase source at acceptable ripple levels.
Another object of the present invention is to provide an improved apparatus for powering x-ray tubes that enables operation with x-ray exposures arranging from repetitive short duration exposures to continuous exposures.
A further object of the present invention is to provide an improved high voltage power supply for x-ray generating tubes preferably operated from a single-phase power source and which is compatible with x-ray exposure detection apparatus such as a television-type camera tube.
Still another object of the present invention is to provide an improved high voltage power supply for x-ray generating tubes and which is characterized by suppression of the inverse high voltage cycle, thus permitting short exposures, yet resetting the magnetic core of the high voltage transformer is accomplished.
Another object of the present invention is to provide apparatus for generating x-ray exposures, which apparatus is characterized by improved simplicity, improved ripple factor and reduced cost.